proceedings of 30th european space thermal analysis …...world space observatory- ultraviolet...

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Appendix C

World Space Observatory-UltravioletThermal Analysis of Spacecraft Electronics

Samuel Tustain(RAL Space, United Kingdom)

30th European Space Thermal Analysis Workshop 5–6 October 2016

36 World Space Observatory-Ultraviolet — Thermal Analysis of Spacecraft Electronics

Abstract

The World Space Observatory-Ultraviolet (WSO-UV) is an upcoming mission led by Roskosmos thataims to provide a major space observatory operational at ultraviolet wavelengths. RAL Space is workingin collaboration with e2v on the World Space Observatory UV Spectrographs (WUVS) instrument, withRAL Space being primarily responsible for the design, build and testing of the Camera Electronics Box(CEB) that drives the instrument.This work at RAL Space follows on from previous electronics box projects on spacecraft such as theNASA Solar Dynamics Observatory (SDO) and the Geostationary Operational Environmental SatelliteR Series (GOES-R). Thermal analysis of the CEB provides a difficult challenge, since in order to bemeaningful the analysis must capture the hot spots within the electronics that are caused by high powerdissipating components on the printed circuit boards. The thermal characteristics of these componentsare often poorly defined, which therefore introduces uncertainty in the results. The requirement to de-rate component temperature limits in accordance with product assurance standards such as ECSS addsadditional challenge, since it significantly reduces any thermal margin within the design.With the dissipated heat loads generated by on-board electronics expected to steadily increase ashardware becomes more sophisticated, these are issues that are likely to become more prevalent forfuture space missions. This talk will examine the rationale behind the modelling of the CEB, discusspossible thermal management solutions and describe the ways in which uncertainty is being defined andaccounted for within the analysis.


Samuel TustainSpacecraft Thermal Engineer

STFC Rutherford Appleton Laboratory

World Space Observatory-Ultraviolet (WSO-UV)

Thermal Analysis of Spacecraft Electronics

30th European Space Thermal Analysis Workshop, 5th-6th October 2016

Outline

• WSO-UV Overview• WUVS Instrument• Camera Electronics Box (CEB)• Heritage• Analysis• Uncertainty and Mitigation Strategies• Testing• Future

World Space Observatory-Ultraviolet — Thermal Analysis of Spacecraft Electronics 37


WSO-UV Overview• Also known as Spektr-UV• Led by Roskosmos, with European

involvement• Launch currently planned for 2021• Key objectives:

– Continue to provide UV observation post-Hubble

– To improve on Hubble– Study formation and evolution of our

galaxy– Study exoplanet atmospheres and

transits• Contains a suite of instruments, including the

WSO-UV Spectrographs (WUVS)– e2v are designing the cryostat and CCD

assembly, RAL Space are designing the camera electronics box (CEB)

Image credit: An Introduction to the WSO-UV Spectrographs, Hermanutz et al, 2012

WUVS Instrument

Image credit: WSO-UV Spanish Team Web Page: http://www.wso-uv.es/index.php?id=12



WUVS Instrument

Camera Electronics Box

(CEB)

Interconnection Module (ICM)

Radiation Receiver

RAL Space Heritage• NASA Solar Dynamics Observatory

(SDO)– Provided flight electronics for two

of three instruments• NASA Geostationary Operational

Environmental Satellite – R Series (GOES-R)

• Initially planned to re-use the GOES-R design for the WSO CEB– Unfeasible due to ITAR restrictions

Image credit: NASA

Image credit: NASA

GOES-R Camera Electronics Box



Camera Electronics Box (CEB)





Thermal Challenges

• The CEB sits on a thermal plate that varies between -25 ⁰C and 50 ⁰C during the mission

• The total power dissipation for the CEB is 14.7 W– This must be conducted away via the base– Radiated heat flows to/from the CEB are assumed negligible

• The PCB components have defined temperature limits, which are then de-rated by 40 ⁰C according to ECSS standards

• Compliance with this must be analytically demonstrated, with qualification and uncertainty margins included

• The analysis must therefore capture the hot spots on the CEB caused at the components



Thermal Model

• Constructed using ESATAN-TMS r7sp2

• Submodels representing the structure and each of the PCBs

• Simple ‘Enclosure’ type radiative case to capture radiative couplings

• Conservative modelling rationale– Lots of uncertainty in

modelling PCB components

• In-plane thermal conductivity is calculated as a function of copper thickness (tCu) and overall thickness (tOv):

• Through-thickness conductance is ignored due to low thickness

• Conformance coating (ε = 0.878) is assumed

PCB Modelling

Experimental Determination of Thermal Conductivity of Printed Wiring Boards, K. Azar and J.E Graebner, 1996

385 0.87



• Components with either large surface area or large power dissipation are modelled.– Smaller components are accounted for by applying their

dissipations directly to the PCB• Each component comprised of junction (where heat is generated) and

casing.– Junction-to-case conductance generally found in datasheets

(although not always!)– Case-to-board conductance rarely found, and therefore estimated

Component Modelling

Junction Case

Board

Case-to-board Conductance

• Estimated based on the number of pins and pin dimensions:

• Kovar (16 Wm-1K-1) assumed for all pins• Area and number of pins varies from component to component• Pin lengths are estimated based on the bending jig that RAL uses



Uncertainty

• There are large uncertainties in this method, due to a lack of information from component manufacturers

• Characterising this in simple terms is difficult, because it varies from component to component

• In accordance with MIL-STD-1540, an uncertainty margin of +17 ⁰C has been applied– Based on experimental data– General practice on instrument projects until a thermal

balance test has been performed

ResultsComponent

Case Temperature

(⁰C)

Junction Temperature

(⁰C)

DeratedMaximum Junction

Temperature (⁰C)

Junction Margin

(⁰C)

IC100 66.2 70.9 85 14.1IC200 62.2 62.7 85 22.3IC204 87.9 95.6 110 14.4IC205 84.6 91.6 110 18.4IC206 88.2 95.9 110 14.1IC207 83.7 90.3 110 19.7IC214 56.4 56.4 85 28.6IC215 57.3 58.2 85 26.8IC217 68.6 69.3 110 40.7IC218 60.2 60.8 110 49.2IC220 88.0 95.3 110 14.7IC224 59.2 59.8 110 50.2IC400 61.5 62.8 85 22.2IC404 60.6 61.9 85 23.1IC502 59.4 65.4 110 44.6IC507 94.5 97.0 110 13.0IC508 54.4 54.4 110 55.6IC509 79.7 81.2 110 28.8IC510 67.9 68.6 110 41.4IC511 60.4 63.1 85 21.9IC702 59.1 65.1 110 44.9IC707 94.2 96.7 110 13.3IC708 53.9 53.9 110 56.1IC709 78.4 79.8 110 30.2IC710 68.5 69.3 110 40.7IC711 60.1 62.8 85 22.2IC900 68.9 69.7 110 40.3

This uncertainty presents issues, as some of the components are predicted to be within this margin during the hottest case (thermal plate at 50 ⁰C)



Mitigation Strategies

• Thermal filler– Improves case-to-board conductance, and analysis

suggests significant temperature reductions– However it’s messy and complicates the assembly process

• Testing– Conduct a thermal balance case during qualification

thermal vacuum testing– Determines suitability of uncertainty margin

Testing

• Test carried out last month on Engineering Qualification Model (EQM)

• Thermocouples attached to problematic components

• Results demonstrate compliance with requirements, and components were cooler than the analysis predicted– Analysis too pessimistic?– Uncertainty approach

unsuitable?



Future

• The thermal balance case has confirmed that thermal filler is not required for the flight model

• Correlation of thermal model required• Future approach for uncertainty is challenging

– Root sum squared (RSS)?– Difficult to accurately characterise individual

sources of uncertainty

pn

kikpi TT

1

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Contact Details

Samuel TustainThermal Engineering Group

Email: [email protected]



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